This invention relates to steelmaking and iron ore. Steelmaking is the largest metallurgical industry in the world and since 2007 global production of iron ore to feed that industry has exceeded 2 billion tons per year. The ore has to be processed for size and grade to meet input specifications for a range of reduction processes that make metallic iron that is then further processed to make steel.
Steel is currently produced by the Blast Furnace/Basic Oxygen Furnace (BF-BOF) route, or by Electric Arc Furnaces (EAF). The BF-BOF route has high energy consumption and adverse environmental impacts, and consequently, although current world production is divided roughly 2:1 in favor of the BF-BOF route, the EAF industry is growing rapidly and is expected to surpass BF-BOF production in the foreseeable future. This will require increased production of Direct Reduced Iron (DRI).
The BF-BOF route relies on iron ore with coal as the energy source, while EAFs use mainly recycled scrap steel and electric power.
Making pig iron in Blast Furnaces generates over 1.5 tons of carbon dioxide per ton of iron. In 2014 the global steel industry released over 1.8 billion metric tons of carbon dioxide into the atmosphere.
The EAF route is more environmentally friendly and there is a growing demand for direct reduced iron (DRI) products that can be fed directly into electric arc furnaces.
Feed for the blast furnace must have carefully controlled size and strength properties and is available as lump ore, sinter or pellets. In 2014, the relative weights of iron ore materials fed to blast furnaces were approximately: lump ore 12%, sinter 54% and pellets 34%. The blast furnace consumed 94% of the iron ore delivered to the global steel industry.
Direct Reduction (DR) technologies that convert iron ore into solid iron products fall into three main categories, shaft furnaces (Midrex, HYL), rotary kiln furnaces (Inmetco, Fastmet) or fluidized bed furnaces (FINMET). There is also considerable interest in developing iron nugget technology (ITmk3) that uses pellets mixed with solid reductants that are heated and reduced to iron nodules in rotary grate furnaces. DR shaft furnaces and rotary kiln furnaces require lump ore or pellet feeds while fluidized bed furnaces, by using iron ore fines directly, have the advantage of avoiding the need for pelletization. The production of iron by DRI is a growing industry and has great potential, but currently consumes only 6% of the total global iron ore production and correspondingly accounts for only 6% of global iron production.
With increasing demand for steel, driven by population growth, but more importantly by the increase in standard of living in developing countries, there is considerable interest in the development of improved or novel DR technologies. One avenue is the development of DR processes using iron ore fines such as the current AISI/DOE sponsored project at the University of Utah.
Furthermore, all current DR processes rely on the supply of separate heat sources fired by fossil fuels. By contrast, the technology presented in this patent uses iron ore fines and generates the heat required to carry out the reduction reactions internally. The result is simple reactor geometry, reduced environmental impact and reduced capital and operating costs.
For operation with natural gas as the reducing gas, savings compared to current DT processes are approximately 30% without off-gas credit and over 45% with off-gas credit. Cost savings compared to the BF production of pig iron are approximately 25% without off-gas credit and 44% with off-gas credit. Furthermore, the carbon dioxide production per ton of iron is about one third that of the blast furnace. Currently, approximately 88% of global iron ore consumption is processed in pellet or sinter plant furnaces with natural gas being the predominant fuel. If an IFDR plant using natural gas as the reducing gas is installed next to these furnaces the IFDR hot combustible off gases can be used as a supplementary fuel.
By using hydrogen as the sole reducing agent, the carbon dioxide produced by all current iron making technologies is eliminated. Operating cost estimates compared to currently operating commercial DR plants, indicate savings over 40%. Cost savings compared to the BF production of pig iron are over 50%.
With increasing concern about global warming there is great interest in reducing carbon dioxide emissions and moving toward a hydrogen economy. Although moving from coal to natural gas in the steel industry provides significant reductions in carbon dioxide emissions any carbon based fossil fuel will generate carbon dioxide. For this reason even though natural gas based DR technologies are a move in the right direction they will eventually have to be replaced with processes using hydrogen as the reducing gas.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. § 1.56(a) exists.